Field of the Invention
The present invention relates to a gas sensor element and a gas sensor used preferably for detecting the concentration of a particular gas contained in, for example, combustion gas or exhaust gas of a combustor, an internal combustion engine, etc.
Description of Related Art
Conventionally, a gas sensor is used for detecting the concentration of a particular component (oxygen, etc.) in exhaust gas of an internal combustion engine. As shown in FIG. 6, this gas sensor has a gas sensor element 1000 provided therein. The gas sensor element 1000 includes a laminate of a detecting element section 1300 and a heater section 1200. The detecting element section 1300 has a cell composed of a solid electrolyte body 1300c, and a pair of electrodes 1300a and 1300b disposed on the solid electrolyte body 1300c. The heater section 1200 is configured such that a heater 1200h is provided in an insulator and generates heat through application of electricity thereto. Heat generated by the heater 1200h activates the solid electrolyte body 1300c, whereby detection by the gas sensor element 1000 is enabled.
Meanwhile, the gas sensor element 1000 may be exposed to poisoning substances, such as silicon and phosphorus, contained in exhaust gas and may suffer adhesion of water droplets contained in exhaust gas. Thus, in order to trap poisoning substances and to prevent direct contact of water droplets with the gas sensor element 1000, the outer surface of the gas sensor element 1000 is covered with a porous protection layer 1400. That is, in the laminate, a forward end portion to be exposed to gas to be measured (exhaust gas) is entirely covered with the porous protection layer 1400 (refer to Patent Document 1). Conventionally, the porous protection layer 1400 is formed on a forward end portion of the gas sensor element 1000 at least in the entire region which has a temperature of 200° C. or higher in the course of use.